1. Field of the Invention
The present invention relates to an inspection device and a method of inspecting a positional deviation in a predetermined XY-plane of a top position of a convex surface of a protruding portion formed on a flat member and a deepest position of a concave surface constituting a back surface of the convex surface.
2. Related Background Art
When, for example, forming a protruding portion on a flat metal sheet, a method like pressing is adopted, in which male and female dies are used. When forming a member of a flat configuration with a protruding portion from a material of a relatively low melting point, a method like injection molding is adopted, in which male and female molds are used. Usually, in a protrusion obtained by such forming methods, assuming that the plane in which the protruding portion is formed is one defining XY-coordinates, it is considered that the XY-coordinates of the top position of the convex surface side and the XY-coordinates of the deepest position of the concave surface side coincide with each other. Even if a positional deviation is generated in these coordinates, the adverse effect thereof is regarded as substantially negligible, and the member obtained is used as it is.
A specific example of a protruding portion on a metal plate obtained by pressing is a dimple formed in a magnetic head of a hard disk drive (see JP 06-215511 A or JP 11-185416 A). Such a dimple consists of a protruding portion of a configuration substantially constituting a part of a spherical surface obtained by performing pressing on a thin metal plate with large spring constant called a load beam. In a hard disk drive, this dimple serves to stabilize the floating attitude of a magnetic head slider that effects recording and reproduction of information to and from a magnetic recording medium while floating over the magnetic recording medium while maintaining a minute gap therebetween.
In the case of a dimple in a magnetic head as mentioned above, the magnetic head slider supported by the dimple has recently been reduced more and more in size and weight. To support this small and light member in a stable manner, it is necessary to accurately measure, for example, the XY-coordinates of the top position of the convex surface of the dimple, and make the XY-coordinates coincide with the XY-coordinates of the center of the magnetic head slider. However, due to the construction of a magnetic head, it is rather difficult to directly measure the dimple top position when mounting the magnetic head slider. Therefore, in some cases, the XY-coordinates of the deepest position of the dimple concave surface, which are easier to measure, are adopted instead of the XY-coordinates of the top position of the convex surface.
As stated above, there may be, if slight, a deviation between the XY-coordinates of the top position of the dimple convex surface and those of the deepest position of the dimple concave surface. When the floating amount of the magnetic head slider is further reduced, and a further improvement in terms of stability in attitude while floating is required, it is necessary to evaluate this deviation amount, and take the deviation amount into consideration when mounting the magnetic head slider.
As described above with reference to the case of the dimple of a magnetic head, when a protruding portion is formed on a flat member, it is necessary to evaluate a positional deviation between the top position of the convex surface and the deepest position of the concave surface. However, when an attempt is made to control the fixing positions, mounting conditions, attitudes, etc. of other members by means of this protruding portion, the following problem is involved: in many cases, when actually controlling the fixing positions, etc. of other members, the protruding portion comes into contact with the other members, is hidden behind the other members, etc., thus making it difficult to directly measure the top position of the convex surface of the protruding portion. Thus, when the requisite accuracy for the fixing positions, etc. becomes higher, it will be inevitably necessary to previously obtain the relationship between the XY-coordinates of the top position of the convex surface and those of the deepest position of the concave surface regarding the protruding portion as described above, and to obtain, at the time of control, the requisite XY-coordinates of the top position of the convex surface from the actual measurement values of the deepest position of the concave surface, which are easier to measure.
Further, if the positional deviation between the XY-coordinates of the top position of the convex surface and those of the deepest position of the concave surface is to be eliminated or mitigated, it will be necessary to improve, for example, the positional accuracy of the male and female dies pressed together in the pressing process. However, it is rather difficult to directly obtain the positional accuracy of the top position of the convex surface of the male die and the deepest position of the concave surface of the female die during pressing, and it would be easiest and most efficient to evaluate the positional accuracy from the product actually obtained by the pressing. Usually, it is not easy to ascertain the arrangement of the convex surface top position and the concave surface deepest position of this product by simultaneously photographing them with a single camera, or to ascertain their respective positions by means of a single measurement system. Given the fact that the positional accuracy required in such cases has not been so high, no definite method for such measurement has been established as yet.